The present disclosure relates to static eliminating device configured to irradiate an image carrier with static eliminating light to statically eliminate the image carrier and electrophotographic image forming apparatuses with the static eliminating device.
Electrophotographic image forming apparatuses are required to reduce the parts cost and the size of the apparatus housing and also required so that a photosensitive drum serving as an image carrier in the image forming apparatus has the effect of reducing the production of a ghost image due to exposure memory on the surface of the photosensitive drum. To reduce the production of a ghost image due to exposure memory, it is necessary to irradiate a region of the photosensitive drum having undergone image transfer with static eliminating light to statically eliminate the surface of the photosensitive drum.
Generally, a static eliminating device is disposed between a drum cleaning device configured to remove deposits, such as residual toner, on the surface of the photosensitive drum and a charging section configured to charge the surface of the photosensitive drum. However, when the image forming speed is increased, the linear speed (peripheral speed) of the photosensitive drum is also increased to significantly shorten the time from static elimination to charging. As a result, trapped carrier (charge) remains in the photosensitive layer on the photosensitive drum, which makes it likely to produce a ghost image due to exposure memory that will degrade the image quality.
To prevent the production of a ghost image due to exposure memory, an image forming apparatus is proposed in which a static eliminating device is disposed upstream of the cleaning device in the rotational direction of the photosensitive drum to secure a time enough to vanish the trapped carrier within the period from static elimination to charging.
The static eliminating device, if disposed upstream of the cleaning device in the rotational direction of the photosensitive drum, is located close downstream of a transfer section. Therefore, untransferred toner having been left untransferred to a paper sheet and toner scattering after the transfer to the paper sheet may adhere to a light-emitting part serving as a static eliminating light source of the static eliminating device. To prevent the adhesion of toner to the light-emitting part, the above image forming apparatus with the static eliminating device disposed upstream of the cleaning device in the rotational direction of the photosensitive drum employs a structure in which a partition member is provided between a paper conveyance path and the static eliminating device and an opening is formed between the partition member and the housing of the static eliminating device to open facing the surface of the photosensitive drum and allow static eliminating light to pass therethrough.
However, in the static eliminating device built in the above image forming apparatus, the space between the partition member and the housing of the static eliminating device, i.e., the opening for passage of the static eliminating light, is restricted by the size (diameter) of the photosensitive drum and the paper conveyance path. Therefore, it is difficult for the opening to secure a sufficient vertical space in the circumferential direction of the photosensitive drum. For this reason, a substrate on which the light-emitting part of the static eliminating device is mounted needs to be disposed in parallel with the outside surface of the housing. In addition, in the above image forming apparatus and its static eliminating device, the partition member is connected (fixed) at the proximal end to the housing but the other end thereof is a free end.
Furthermore, it is conceivable that the static eliminating device is provided with a restricting protrusion disposed between the surface of the photosensitive drum and the substrate and extending toward the partition member in the thickness direction of the substrate. With the use of such a structure including the restricting protrusion, the position of the partition member can be restricted by the restricting protrusion to facilitate the keeping of the opening for passage of static eliminating light. However, static eliminating light becomes likely to be shielded by the restricting protrusion to decrease the amount of static eliminating light passing through the opening. This presents a problem of uneven intensity distribution of static eliminating light along the axial direction of the photosensitive drum.